A leading cause of blindness is the inability to introduce drugs or therapeutic agents into the eye and maintain these drugs or agents at a therapeutically effective concentration therein for the necessary duration. Systemic administration may not be an ideal solution because, often, unacceptably high levels of systemic dosing is needed to achieve effective intraocular concentrations, with the increased incidence of unacceptable side effects of the drugs. Simple ocular instillation or application is not an acceptable alternative in many cases because the drug may be quickly washed out by tear-action or is depleted from within the eye into the general circulation.
A better solution would be to provide a delivery device which can be implanted into the eye such that a controlled amount of desired drug can be released constantly over a period of several days, or weeks, or even months. Some such devices have been reported in the prior art. See, for example, U.S. Pat. No. 4,853,224, which discloses biocompatible implants for introduction into an anterior segment or posterior segment of an eye for the treatment of an ocular condition. U.S. Pat. No. 5,164,188 discloses a method of treating an ocular condition by introduction of a biodegradable implant comprising drugs of interest into the suprachoroidal space or pars plana of the eye. See also U.S. Pat. Nos. 5,824,072, 5,476,511, 4,997,652, 4,959,217, 4,668,506, and 4,144,317.
Many of the above-disclosed devices comprise of multiple layers and are complicated in their design and manufacture. Moreover, some of the devices are osmotically driven wherein an osmotic gradient is responsible for the drug efflux from the device. In some cases, the drug release is controlled by an ionic gradient. These devices thus must necessarily comprise these additional osmotic or ionic agents, which may not be compatible with the ocular environment. Thus, there is a need for a biocompatible ocular implantable controlled release drug delivery device that is simple in design, does not require an osmotic or ionic agent for drug efflux and yet accomplishes the objectives of prolonged and uninterrupted ocular drug delivery. This invention meets this need.